City of Sarasota Sarasota County US Army Corps of Engineers 22 October 2013 Sarasota Florida Presented by Milan A Mora PE Jason Engle PE James LaGrone Kathleen McConnell ID: 791755
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SARASOTA COUNTY – LIDO KEY HURRICANE & STORM DAMAGE REDUCTION PROJECT
City of SarasotaSarasota CountyUS Army Corps of Engineers22 October 2013Sarasota, FloridaPresented by: Milan A. Mora, P.E. Jason Engle, P.E. James LaGrone Kathleen McConnell
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US ARMY CORPS OF ENGINEERS | JACKSONVILLE DISTRICT
Information Presentation
BOCC Joint Meeting
Slide2OVERVIEW – PROJECT SCOPE
Authorized WRDA 1999 Authority was contingent on a feasibility assessment of the project.2002 Feasibility Study with Environmental Assessment (amended April 2004) determined that project was technically sound, environmentally acceptable and economically justified.
BUILDING STRONG
®
US ARMY CORPS OF ENGINEERS | Jacksonville District
2
1971
2006
1986
Slide3OVERVIEW – PROJECT FEATURES
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3
80 ft Design
Berm
over 1.6 miles
D2
C
B
3 Proposed Sand Sources
Groin Field
(
3)
Project Scope
Project Length (ft) = 8,280 (R-35 to R43)
Design
berm
elevation (ft) = +5 NGVD
Approximately 460,000 cy of design and 615,000 cy
of advance material (1,075,000 cy for Initial Const)
Three groins along the southern portion
Borrow Areas: Big Sarasota Pass (BSP) & New Pass
5-year nourishment interval over 50-year life
615,000 cy required for each re-nourishment
Slide4PROJECT PLAN
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4
1)
Placement:
Place approximately 1.1M CY of sand on Lido Key
2) Source:
Obtain
Sediment for Nourishment of Lido Key
Egmont Key (Tampa Bay)
Offshore of Longboat Key
Ebb Shoal at Big Sarasota Pass (BSP)
New Pass – Future
3) Retain
:
Construct Three (3) groins at the south end of Lido Key
Slide5PLACEMENT – LIDO KEY
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MHW Line - Design
Berm
2013 MHW Line
MHW Line - Advanced
Berm
FDEP Monument R-39
(Lime Tree Resort/Condos)
150’
150’
80’ Design
Berm
@ 5’
Advanced
Berm
Slide6SOURCE – BSP BORROW AREAS
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6
D2
C
B
Slide7RETAIN – SOUTHERN GROINS
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7
Retain
Beach Nourishment
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PROJECT PLAN –
BORROW AREA QUESTIONS?
Slide9BORROW AREAS?
What are the proposed borrow area footprints?
How will this affect Big
Sarasota Pass morphology?
How will this affect Siesta Key?
What
are
the effects
on the navigation channel?
Slide10alt d2, C, B – 1.7
mcY
BORROW
AREA FOOTPRINTS
D2
C
B
Slide11Flood Marginal Channel
Relic ChannelUpdrift ShoalMain Ebb Channel
Distal Lobe
Downdrift
AttachmentFlood Marginal Channel
In the long term:
These areas will be deeper
BSP MORPHOLOGY
Existing Conditions
Slide12% Increase in wave energy here and here
% Decrease in wave energy here and here
Results from the CMS morphologic model yields No indication of increased erosion over the Existing Condition at Siesta Key
HOW WILL THIS AFFECT SIESTA KEY?
Slide13Navigable water greater than 6m depth
without projectNavigable water greater than 6m depth with projectNo significant difference in navigable water depths without and with project
EFFECT ON CURRENT
NAVIGATION?
Slide14BUILDING STRONG
®US ARMY CORPS OF ENGINEERS | Jacksonville DistrictPROJECT PLAN –
SOUTHERN GROINS
GENERAL
QUESTIONS?
Slide15SOUTH LIDO KEY GROINS
What are the plans for the groins?How long are they?How much space is between them?How big are they?
Can
I walk along the beach?
Can I swim in the surf zone?Can I navigate past them?
Slide16350’
500’460’
600’
800’
2004
Present Day
HOW LONG? HOW MUCH SPACE IN BETWEEN ?
Slide17HOW BIG ARE THEY?
Slide18CAN I WALK ALONG THE BEACH?
Slide19CAN I SWIM IN THE SURF ZONE?
CAN I NAVIGATE PAST THEM?
Slide20BUILDING STRONG
®US ARMY CORPS OF ENGINEERS | Jacksonville DistrictPROJECT PLAN –
SOUTHERN GROINS
HYPOTHETICAL
QUESTIONS?
Slide21What if the groins do not work?
What is the effect on Lido Beach?What is the effect on Siesta Key?How will the groins affect the ebb shoal in BSP?Why nourish the beach if we are installing structures?
Slide22Downdrift Effects
Sediment Bypassing to BSP Ebb Shoal
Groins are constructed to anchor the nourishment template – not to intercept
Sediment at the expense of downdrift beaches or ebb shoal morphology!
WHAT IS THE EFFECT ON LIDO KEY?
WHAT IS THE EFFECT ON SIESTA KEY?
Slide23How will the groins affect the ebb shoal in BSP?
Downdrift Effects
Sediment Bypassing to BSP Ebb Shoal
Adequate sediment bypassing at the seaward end of the groin structures will deter the growth of a
crescentic
shoreline . Adequate bypassing to the Ebb Shoal ensures that BSP will maintain its morphology – seen by lack of erosion in the shoal itself
Slide24Why nourish the beach if we are installing structures?
Groins are constructed to anchor the nourishment template – not to intercept sediment at the expense of downdrift beaches or ebb shoal morphology!Groin construction without an associated nourishment project can lead to downdrift erosion and a lack of sediment supply to downdrift systemsThe groins are designed to work with the nourishment design template – should the beach erode shoreward of the design template, Emergency measures are implemented
Slide25Groins – Anchor the Nourishment
Beach Nourishment
Retain
1981
1983
1986
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Questions/Discussions
Milan A. Mora, P.E.Project ManagerJacksonville DistrictWater Resources Branch701 San Marco Boulevard
Jacksonville, FL 32207
904-232-1454
millan.a.mora@usace.army.mil
LIDO KEY SPP